Wireless telecommunication systems are well known in the art. In order to provide global connectivity for wireless systems, standards have been developed and are being implemented. One current standard in widespread use is known as Global System for Mobile Telecommunications (GSM). This is considered as a so-called Second Generation mobile radio system standard (2G) and was followed by its revision (2.5G). GPRS and EDGE are examples of 2.5G technologies that offer relatively high speed data service on top of (2G) GSM networks. Each one of these standards sought to improve upon the prior standard with additional features and enhancements. In January 1998, the European Telecommunications Standard Institute—Special Mobile Group (ETSI SMG) agreed on a radio access scheme for Third Generation Radio Systems called Universal Mobile Telecommunications Systems (UMTS). To further implement the UMTS standard, the Third Generation Partnership Project (3GPP) was formed in December 1998. 3GPP continues to work on a common third generational mobile radio standard.
A typical UMTS system architecture in accordance with current 3GPP specifications is depicted in FIG. 1. The UMTS network architecture includes a Core Network (CN) interconnected with a UMTS Terrestrial Radio Access Network (UTRAN) via an interface known as Iu which is defined in detail in the current publicly available 3GPP specification documents. The UTRAN is configured to provide wireless telecommunication services to users through wireless transmit receive units (WTRUs), known as User Equipments (UEs) in 3GPP, via a radio interface known as Uu. The UTRAN has one or more Radio Network Controllers (RNCs) and base stations, known as Node Bs in 3GPP, which collectively provide for the geographic coverage for wireless communications with UEs. One or more Node Bs are connected to each RNC via an interface known as Iub in 3GPP. The UTRAN may have several groups of Node Bs connected to different RNCs; two are shown in the example depicted in FIG. 1. Where more than one RNC is provided in a UTRAN, inter-RNC communication is performed via an Iur interface.
Communications external to the network components are performed by the Node Bs on a user level via the Uu interface and the CN on a network level via various CN connections to external systems.
In general, the primary function of base stations, such as Node Bs, is to provide a radio connection between the base stations' network and the WTRUs. Typically a base station emits common channel signals allowing non-connected WTRUs to become synchronized with the base station's timing. In 3GPP, a Node B performs the physical radio connection with the UEs. The Node B receives signals over the Iub interface from the RNC that control the radio signals transmitted by the Node B over the Uu interface.
A CN is responsible for routing information to its correct destination. For example, the CN may route voice traffic from a UE that is received by the UMTS via one of the Node Bs to a public switched telephone network (PSTN) or packet data destined for the Internet. In 3GPP, the CN has six major components: 1) a serving General Packet Radio Service (GPRS) support node; 2) a gateway GPRS support node; 3) a border gateway; 4) a visitor location register; 5) a mobile services switching center; and 6) a gateway mobile services switching center. The serving GPRS support node provides access to packet switched domains, such as the Internet. The gateway GPRS support node is a gateway node for connections to other networks. All data traffic going to other operator's networks or the internet goes through the gateway GPRS support node. The border gateway acts as a firewall to prevent attacks by intruders outside the network on subscribers within the network realm. The visitor location register is a current serving networks ‘copy’ of subscriber data needed to provide services. This information initially comes from a database which administers mobile subscribers. The mobile services switching center is in charge of ‘circuit switched’ connections from UMTS terminals to the network. The gateway mobile services switching center implements routing functions required based on current location of subscribers. The gateway mobile services also receives and administers connection requests from subscribers from external networks.
The RNCs generally control internal functions of the UTRAN. The RNCs also provides intermediary services for communications having a local component via a Uu interface connection with a Node B and an external service component via a connection between the CN and an external system, for example overseas calls made from a cell phone in a domestic UMTS.
Typically a RNC oversees multiple base stations, manages radio resources within the geographic area of wireless radio service coverage serviced by the Node Bs and controls the physical radio resources for the Uu interface. In 3GPP, the Iu interface of an RNC provides two connections to the CN: one to a packet switched domain and the other to a circuit switched domain. Other important functions of the RNCs include confidentiality and integrity protection.
In a typical cellular communication system, such as UMTS time division duplex (TDD), UMTS frequency division duplex (FDD), each transmitter-receiver link is required to maintain a certain quality-of-service (QoS) level, typically measured in either signal-to-interference ratio (SIR), bit error rate (BER), or block error rate (BLER). Because such systems are generally interference limited, it is desirable for the transmitters to expand the minimal amount of power necessary to maintain the specified link quality.
Various methods of power control for wireless communication systems are well known in the art. An examples of a closed loop power control transmitter system for a wireless communication system is illustrated in FIG. 2. The purpose of such systems is to rapidly vary transmitter power in the presence of a fading propagation channel and time-varying interference to minimize transmitter power while insuring that data is received at the remote end with acceptable quality.
In communication systems such as Third Generation Partnership Project (3GPP) Time Division Duplex (TDD) and Frequency Division Duplex (FDD) systems, multiple shared and dedicated channels of variable rate data are combined for transmission. Background specification data for such systems are found at 3GPP TS 25.223 v3.3.0, 3GPP TS 25.222 v3.2.0, 3GPP TS 25.224 v3.6 and Volume 3 specifications of Air-Interface for 3G Multiple System Version 1.0, Revision 1.0 by the Association of Radio Industries Businesses (ARIB). A fast method and system of power control adaptation for data rate changes resulting in more optimal performance is taught in International Publication Number WO 02/09311 A2, published 31 Jan. 2002 and corresponding U.S. patent application Ser. No. 09/904,001, filed Jul. 12, 2001 owned by the assignee of the present invention.
Generally in loop power control between a transmitter and a receiver, the receiver estimates the quality of the link and reports back to the transmitter using a different link to either increase its transmit power if the link quality is not met or decrease it if the link quality is higher than desired. Because wireless channels are variable, the link quality monitoring is a continual operation where the behavior of the transmitters is continually adapted to the channel conditions.
Link monitoring must be performed both on the forward and the reverse links of a cellular system. In addition to the closed-loop “power-control” task described above, link QoS information may be necessary for other operations, such as in-sync/out-of-sync detection, radio resource management, etc. Accordingly, the link quality operation is very important to the proper performance of most cellular communication systems; however, obtaining an accurate measurement of link quality is a non-trivial task.
The BLER value is a typical desired measurement of the link quality, but accurate estimation of this quantity based on the actual error rates in the received data is not feasible in many cases because of the length of time needed to determine an accurate value. The decoded (post-channel-decoder) BER is often used as a substitute, but in fading channel conditions, there is a reduced relationship between BLER and the BER. A further consideration is that this BER may also take a significant amount of time to compute.
The signal-to-interference ratio (SIR) has often been used in classical (RAKE-receiver) CDMA systems as a QoS estimate because of the ease with which it can be rapidly estimated from the received signal. In systems using linear multi-user detectors, the method for SIR computations that were used in classical CDMA are no longer valid, and methods directed at QoS measurements in such systems are not well understood.